Abstract

We compare the electronic temperatures and the population inversion both below and above the lasing threshold in three quantum-cascade lasers (QCLs) operating at , , and using microprobe band-to-band photoluminescence. In the lasing range, while the ground-statetemperature remains close to the lattice one , the upper radiative state heats up to . From the measured thermal resistance and the power dependence of the ground-state electronic temperature, we get a value of the electron-lattice energy relaxation rate comparable with that typical of midinfrared QCLs.

Received 08 November 2004Accepted 01 February 2005Published online 10 March 2005

Acknowledgments:

This work was partly supported by MIUR (FIRB-RBAU01E8SS), ESA-ESTEC(16863∕02∕NL∕PA), and by AFOSR, NASA, and NSF at MIT. One of the authors (B.W.) would like to thank H. Callebaut for helpful discussions. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed–Martin Company, for the U. S. Dept. of Energy (Contract No. DE-AC04-94AL85000).